1. Field of the Invention
The present disclosure relates to methods of reducing penetration of inflammatory cells into tissue, in particular to methods of reducing extravasation of macrophage cells from blood vessels, methods of preventing, regulating and suppressing inflammatory response, and methods of treating inflammatory states.
2. Description of Related Art
The inflammatory response evolved to protect organisms against injury and infection. Following an injury or infection, a complex cascade of events leads to the delivery of blood-borne leukocytes to sites of injury to kill potential pathogens and promote tissue repair. However, the powerful inflammatory response has the capacity to cause damage to normal tissue, and dysregulation of the innate or acquired immune response is involved in different pathologies. It has long been known that Multiple Sclerosis is an inflammatory disease of the brain, but it is only in recent years that it has been suggested that inflammation may significantly contribute to diseases such as stroke, traumatic brain injury, HIV-related dementia, Alzheimer's disease and prion disease. The recognition of an inflammatory component in the pathology of these and other diseases has come from the development of new techniques and reagents for the study of inflammation biology.
The inflammatory response is a part of innate immunity. Inflammation occurs when tissues are injured by viruses, bacteria, trauma, chemicals, heat, cold, or any other harmful stimuli. Chemicals, such as bradykinin, histamine, and serotonin, are released by specialized cells and attract tissue macrophages and white blood cells to localize in an area to engulf (phagocytize) and destroy foreign substances. A byproduct of this activity is the formation of pus—a combination of white blood cells, bacteria, and foreign debris. The chemical mediators released during the inflammatory response give rise to the typical findings associated with inflammation.
Inflammation constitutes the body's response to injury and is characterized by a series of events that includes the inflammatory reaction per se, a sensory response perceived as pain, and a repair process. The inflammatory reaction is characterized by successive phases: (1) a silent phase, where cells, including resident cells in the damaged tissue, release the first inflammatory mediators, (2) a vascular phase where vasodilation and increased vascular permeability occur, and (3) a cellular phase, which is characterized by the infiltration of leukocytes to the site of injury. The repair process includes tissue cell division, neovascularization and reinnervation of repaired tissues. In many diseases such as arthritis, inflammatory bowel disease, and asthma, the inflammatory process is not appropriately regulated. As a result, significant tissue dysfunction (leading to the generation of the symptoms that typify these diseases), and tissue re-structuring occur (e.g., fibrosis) that can further impair tissue function.
The very first event of the inflammatory reaction, the “silent phase” is based upon the reaction of cells and resident cells of the damaged tissue. These resident cells release mediators, such as nitric oxide (NO), histamine, kinins, cytokines, or prostaglandins. The release of these vasomotor mediators from resident cells leads to the second phase of the inflammatory reaction: the vascular phase. Vascular tone and permeability are regulated by an endothelial-dependent mechanism involving the release of nitric oxide. Certain agonist signal to sensory afferents, including the release of neuropeptides which are known to act on vascular beds to induce vasodilation and increased permeability. Increased vasodilatation and permeability provoke plasma leakage from the blood to the inflamed tissues, and facilitate the passage of leukocytes from the blood flow to the tissues.
The third phase of the inflammatory process is the cellular phase, which is characterized by the arrival of leukocytes circulating in the blood. In order to be recruited to the site of inflammation, circulating leukocytes roll onto the venular endothelial surfaces, adhere to the endothelium, and then transmigrate across the endothelial barrier. The process by which cells leave the blood stream and penetrate tissue parenchyma is known as extravasation. The events of rolling, adhesion, and transmigration (extravasation) are regulated by several cell adhesion molecules, known as CAMs and receptor molecules expressed by the endothelium and the leukocytes.
The inflammatory response to tissue damage may be of great value. By isolating the damaged area, mobilizing effector cells and molecules to the site, and—in the late stages—promoting healing, inflammation may protect the body. However, inflammation is more often associated with pain, injection and diseased states. Often the inflammatory response is out of proportion to stimulus which activated the response. The inflammatory process inevitably causes tissue damage and is accompanied by simultaneous attempts at healing and repair. Tissue destruction is caused by both the caustic agents and by the inflammatory process itself. The result can be more damage to the body than the agent itself would have produced. For example, all the many types of allergies and many of the autoimmune diseases are examples of inflammation in response to what should have been a harmless, or at least a noninfectious, agent. Some examples of chronic inflammatory diseases include Asthma, Rheumatoid Arthritis (RA), Multiple Sclerosis (MS), Systemic Lupus Erythematosus (SLE), psoriasis, and Chronic Obstructive Pulmonary Disease (COPD). In many of these cases, the problem is made worse by the formation of antibodies against self antigens or persistent antigens from smoldering infections. Additionally, any disease with an inflammatory component may be treated by a better understanding of the immune system and the disease-fighting responses to toxins, injury, viruses and bacteria. Recently, it has been shown that inflammation has been link to cardiovascular diseases.
Traditional therapeutics for the treatment of inflammation include anti-inflammatory agents and steroids. Inappropriate inflammation can be treated with steroids like the glucocorticoid cortisol, nonsteroidal anti-inflammatory drugs (NSAIDs) like aspirin and ibuprofen, and a number of proteins produced by recombinant DNA technology.
The NSAIDs achieve their effects by blocking the activity of cyclooxygenase. The body produces several different forms of cyclooxygenase (COX), including COX-1, which is involved in pain, clotting, and protecting the stomach; COX-2, which is involved in the pain produced by inflammation. Most of the NSAIDs inhibit both COX-1 and COX-2. However, some newer drugs, the so-called COX-2 inhibitors, such as rofecoxib (Vioxx®) and celecoxib (Celebrex®) are much more active against COX-2 than COX-1.
Recombinant DNA and monoclonal antibody technology have produced some new therapies that are being enlisted in the battle against damaging inflammation. Examples of these therapeutics include: (1) an IL-1 antagonist that binds and inactivates the IL-1 receptor; (2) etanercept (Embrel®), which a soluble version of the TNF-α receptor, which binds TNF-α preventing it from carrying out its many inflammatory actions; (3) recombinant protein C, which helps the body dissolve the tiny clots that are triggered during inflammation; (4) infliximab (Remicade®), which is a monoclonal antibody that binds to TNF-α, particularly promising against some inflammatory diseases such as rheumatoid arthritis; and (5) the antibody natalizumab (Antegren®; Biogen Inc., Cambridge, Mass.), which functions by blocking the adhesion of immune cells to blood vessels and can inhibit movement of immune cells from the blood into the brain. Several of these therapies carry a severe risk of allowing infections to develop. In fact, the more powerful the anti-inflammatory agents (e.g., glucocorticoids), the greater the risk of infection.
Reducing inflammation and regulating the inflammatory response also is beneficial in the prevention of various cancers and other cell conditions. Chronic inflammation is a recognized cause of cancer. For example, liver cancer is often the sequel to years of inflammation caused by infection hepatitis B or C infection. Lung cancer often is the end stage of years of chronic inflammation caused by inhaled irritants, such as tobacco smoke. Cervical cancer can follow chronic infection and inflammation caused by papilloma viruses and chlamydia. Similarly, bladder, colon, pancreas, stomach, and other cancers may be the final stage of years of inflammation.
The strong link between chronic inflammation and cancer should not be surprising considering that the reactive oxygen species (ROS) liberated during inflammation are powerful DNA-damaging agents. Additionally, increased mitosis in response to inflammation puts more cells at risk of mutations as they replicate their DNA during S phase. Furthermore, apoptosis, the programmed death of damaged cells, is suppressed in inflamed tissue. So precancerous cells with genetic mutations, which should have committed suicide, continue and ultimately develop into cancerous cells. Therefore, the regulation of the inflammatory response including reducing inflammation in tissues is beneficial to the prevention of various cancers.
The penetration of inflammatory cells into and through the parenchyma of tissues is intimately involved in the pathophysiology of numerous disease, injury and inflammatory states. The ability to prevent penetration of inflammatory cells into tissue has beneficial therapeutic effects. It is known that reduction of tissue penetrating inflammatory cells has been accomplished to a degree with steroid, anti-integrin and other anti-inflammatory compounds. The access of cells through the blood vessel wall and into tissues is, in part, dependent upon the extracellular matrix, receptor molecules, CAMs, the cell membranes of the vascular endothelium and the migrating cell. Interfering with one or more of these signals or receptors disrupts the recruitment of inflammatory cells to the tissue. This disruption thus leads to reduced inflammation in the tissue.